Counting circuit employing plural multi-cathode counting tubes



Feb. 23, 1965 c. B. FALCONER 3,171,059

COUNTING CIRCUIT EMPLOYING PLURAL MULTI-CATHODE COUNTING TUBES Filed April 5, 1962 4 Sheets-Sheet 2 d z y m LU 6 LL ll.

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couu'rzuc CIRCUIT EMPLOYING PLURAL MULTI-CATHODB COUNTING TUBES Filed April 5, 1962 4 Sheets-Sheet 3 E Z. l W

INVENTOR. 33' 2 CHARLES B. FALGONER 1 5 BY E z I V ATTORNEYS Feb. 23, 1965 c. B. FALCONER 3,171,059

COUNTING CIRCUIT EMPLOYING PLURAL MULTI-CATHODE COUNTING TUBES 4 Sheets-Sheet 4 Filed April 5, 1962 I ll llll lll III IEIELIFIELLIPILL' 8N8 N3 \NBO 0 N500 -28 985M630 x28 80% 5 3 EH38 108 9000 g 308 98g NNNNN AT TOR NEYS United States Patent C) 3,171,059 COUNTING CIRCUKT EMPLGYING PLURAL MULTI-CATHODE COUNTHNG TUBES Charles B. Falconer, Newton, Mass, assiguor to Laboratory for Electronics, Inc., Boston, Mass, a corporation of Delaware Filed Apr. 5, 1962, Ser. No. 135,385 3 Claims. (Cl. 31584.6)

This invention relates in general to counting tube circuitry and, more particularly, to a counting circuit including a series of cascaded glow transfer tube decades.

Digital counting circuits have come into widespread use both in the computer field itself and in related fields, such as, nuclear electronics, in which digital techniques are employed, Many of these circuits use as the basic counting element a decade unit, which provides an output pulse when it has accumulated ten input pulses. By cascading decade units, a total digital count capacity in the millions can readily be achieved. Thus, if three decade units are cascaded, the total count capacity is 1,000, if six are cascaded 1,000,000, and so forth. With the advent of glow transfer decade tubes, the decade circuit became essentially a single tube.

Decade counter tubes are available in several forms. One form is the type of glow transfer tube considered here, which is also referred to as the three-phase gas tube. The glow transfer tube employs a single anode and multiple cathodes. Thirty cathodes are required, ten of which represent the digits in the decade, ten of which serve as first transfer guides, and ten of which serve as second transfer guides. In operation, high voltage sufficient to maintain a gas discharge between the anode and one of the cathodes is applied across the tube. If one of the cathodes, for example the first digit cathode, is negatively pulsed, the discharge will preferentially occur between that cathode and the anode and, once it has occurred, it will draw sufficient current through the anode resistor to lower the anode voltage below the point at which discharge with another cathode can take place.

A typical geometric configuration for this type of glow transfer tube is one in which each of the digit representing cathodes are separated by a first and a second transfer guide cathode, with the entire cathode array being arranged in a circle about the anode, which is located in the center of that circle. The transfer of the glow discharge from one digit cathode to the next digit cathode is accomplished as follows. A negative pulse is applied to the first transfer guide cathode. The ions in the region of the first digit cathode will tend to drift to adjacent cathodes, and hence the cathode to anode voltage required to initiate a discharge on the first transfer guide adjacent to the first digit cathode is less than the voltage required to initiate a discharge on the remainder of the cathodes. Thus, the discharge will transfer to the first transfer guide following the first digit cathode. Because of the negative signal on this guide, the anode potential will be dropped below the value necessary to sustain the discharge to the first digit cathode. The second transfer guides are now pulsednegatively and, simultaneously or shortly thereafter, the negative pulse is removed from the first transfer guide, and the discharge will transfer from the first transfer guide to the second transfer guide. When the negative pulse is removed from the second transfer guide, the discharge will transfer to the next digit cathode, if the transfer guides are suitably biased. Hence, the transfer of the glow discharge from one digit cathode to the next is a three-step process and for each incoming pulse to be counted, a pair of pulses to the guide cathodes must be generated. The phase relationship of the two pulses must be such that the second negative pulse is generated approximately coincidental with the end of the first negative pulse.

A cascaded decade counter utilizing glow transfer tubes must have pulse advance drive circuitry to generate guide pulses both from the input pulses and for interstage coupling to drive the decades following the first decade. In one such circuit, known in the art, the single trigger pulse to be counted is applied to a univibrator, which provides a square output pulse. The univibrator output pulse is applied directly to the first transfer guides and through an R.C. integrating circuit to the second transfer guides. Thus, the pulses on the second transfer guides are deiayed with respect to those applied to the first transfer guides. For interstage coupling, the output cathode (commonly the zero cathode) is capacitively coupled to a triode, which provides both a direct output and an output through an 7 integrator to the guide cathode on the next stage. Each driving circuit then requires a triode plus seven to ten components. In addition, the appropriate phase relationship between the first guide and the second guide pulses depends upon the critical integrating time constant. Since the time constant required for the various cascaded stages may differ, the complete counter must be designed as a unit and the various interactions between decades allowed for.

It is, therefore, a primary object of the present invention to provide a simple, economical glow transfer drive circuit having reliable and stable operation at high pulse rates, utilizing repetitive circuitry.

It is still another object of the present invention to provide an interstage coupling circuit for cascaded glow transfer tubes which limits the output voltage swing from the output cathodes to a substantially constant value, thus enhancing glow transfer tube reliability and which provides a reliable drive circuit for the glow transfers in the following stage.

Broadly speaking, the circuit of this invention generates a pair of precise square waves in response to each of the input pulses to be counted. The square waves are generated such that the leading edge of the second square wave is precisely aligned with the initiation of the trailing edge of thefirst square wave. The first square wave is applied to the first transfer guide cathodes of the first glow transfer tube of the cascaded series, while the second square wave is applied both to the second transfer guide cathodes of the first glow transfer tube and also to the first transfer guides of the second glow transfer tube. For each input pulse applied to the circuit, the first glow transfer tube advances one digit. On the tenth such advance the glow is returned to the zero cathode, which also serves as an output cathode. Each output cathode is connected to the grid of a triode which is normally biased into the cutoif region. The arrival of the discharge on this output cathode renders the triode conducting. The anode of the triode associated with the first glow transfer tube is capacitively coupled to the second transfer guides of the second glow transfer tube in the cascade and also to the first transfer guides of the third glow transfer tubes in the cascade. With this arrangement every time the discharge arrives at the output cathode of the first glow transfer tube, the second pulse from the pulse generator which caused the transfer to this output cathode is applied to the first guides of the next stage. In addition, because of the arrival of the discharge on the output cathode, a pulse, having a leading edge coinciding with the arrival of'this discharge on the output cathode, is applied to the second guides of the next stage. The pulses applied to the guide cathodes of the second glow transfer tube are then in appropriate sequence to advance the glow discharge in this tube from a digit cathode to the first guide and then to the second guide.

The point at which the voltage on the second guide drops below the voltage necessary to sustain the discharge on this guide will be determined by either the arrival of the next first pulse to the first glow transfer tube or the decay of the second guide pulse at the second glow transfer tube through the coupling time constant. When this occurs, the discharge is transferred to the next digit cathode of the second glow transfer tube.

The second glow transfer tube has associated with it a second triode biased in the same fashion as the triode associated with the first glow transfer tube, and in this instance the grid is connected to the output cathode of the second glow transfer tube. Hence, the arrival of the glow discharge on the output cathode of the second tube renders the associated triode conducting. The anode is again R.C. coupled to the second guide cathodes of the third glow transfer tube, whose first guide cathodes are connected to the second guide cathodes of the second glow transfer tube. The guide pulses applied to the third stage glow transfer tube are then in the same sequential arrangement as those applied to the first and second stages, that is, the pulses applied to the first transfer guide are the second guide pulses frorn the previous stage while the pulses applied to the second guides of the third stage result from the arrival of the discharge in the second stage at its output cathode. .The output from the third glow transfer tube is taken directly from its output or zero cathode.

If it is desired to cascade more than three glow transfer tubes sequentially, the above sequence may be continued under certain limiting conditions which will be described at a later point. Alternatively, the output from the third stage may be provided to a pulse shaping input of the same form as the pulse shaping input to the first glow transfer tube, thus providing another cycle of three cascaded transfer tubes, or the output from the third stage may be provided to the input of any conventional counting systems for operations at lower pulse rates, since the input pulse rate at this point has been scaled down by a factor of 1000.

Other objects and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawing in which:

FIG. 1 is an illustration in schematic form of a circuit in accordance with the principles of this invention;

FIGS. 2A and 2B are waveform timing diagrams applicable to the circuit of FIG. 1;

FIG. 3 is an illustration in schematic form of a circuit in accordance with the principles of this invention for generating the waveforms of FIG. 4; and

FIG. 4 is an illustrative waveform timing diagram when all decades have been represented as having a capacity of three counts, in place of the usual ten, thus enabling a longer effective sequence to be shown.

With reference now specifically to FIG. 1, three glow transfer decade tubes V V and V are serially cascaded. Each of these glow transfer tubes has ten digit cathodes arranged in a circle, and interspersed between each pair of digit cathodes are first and second guide cathodes. The transfer of the glow discharge, as mentioned above, is accomplished in three steps; transfer of the discharge from one digit cathode to the adjacent first guide cathode, transfer of the glow discharge from the first guide cathode to the second guide cathode, and transfer of the discharge from the second guide cathode to the next digit cathode. Each of the glow transfer tubes has a single anode connected through a plate resistor to a positive voltage supply 55. One of the digit cathodes, generally the zero cathode, serves as an output cathode to the next succeeding stage. Thus, turning to glow transfer tube V the anode 20 is connected through resistor 25 to the positive voltage. Nine of the digit cathodes, represented generally at 21, are connected directly to ground, while the tenth cathode, K is connected to the grid of a triode T associated with the first glow transfer tube, V The first guide cathodes are designated schematically as G1 1, and the second or lagging guide cathodes are designated as 61 Similar designations are used with respect to the second and third glow transfer tubes, V and V Thus, the output cathode of tube V is designated K while the first guide cathodes are designated GZ and the second guide cathodes G2 In the third transfer tube, V the output cathode is K while the guide cathodes are shown as GS and G3 Referring now to the associated circuitry, the pulses to be counted are applied to pulse input 11 of a pulse generator 12. In response to each input pulse the pulse generator 12 provides a pair of squarewave output pulses, each one on an independent output, and both on a suitable D.C. base line (bias level) for satisfactory glow tube operation. The squarewave pulse on output 14 is delayed with respect to the squarewave pulse on output 13 such that the leading edge of the squarewave on output 14 is substantially coincident in time with the trailing edge .of.

the squarewave on output 13. Output 13 is connected directly to the first guide cathodes 61 .1, of tube G1, and output 14 is connected both to the second guide cathodes GI of tube V and to the first guide cathodes, GZ of tube V The output cathode K of tube V is connected to the grid 3.0 of triode T Negative bias from a bias voltage supply 32 is applied through resistor 31 to grid 30 as well as cathode K The cathode 27 of triode T is directly grounded and the anode 33 of this triode is connected through plate resistor 34 to B+. An output is taken from the anode 33 of triode T through capacitor 35 to one end of resistor 36. The junction between capacitor 35 and resistor 36 is connected directly to the first guide pins G3 of glow tube V The other end of resistor 36 is connected to the second guide pins, G2 of glow tube V The guide pins G2 of tube V and the guide pins GS of glow tube V are connected through resistors 37 .and 38 respectively to the positive bias voltage supply 40.

A second triode, T associated with tube V is connected in the same fashion as triode T with the grid 42 connected directly to cathode K The anode 43 of triode T is, in this case, however, coupled through capacitor 45 and resistor 46 only to the second guide cathodes (33 of tube V The output cathodes K and K, of transfer tubes V and V respectively are also coupled through resistors 50 and 52 to the negative cathode bias voltage supply 32. The output from the cascade of three glow transfer tubes is taken directly from the cathode K of tube V This output may be utilized in several different ways, as described earlier.

FIGS. 2A and 2B show waveform timing diagrams for two different conditions. In FIG. 2A, the waveform at various points in the circuit is illustrated for the 1,000th pulse; that is, for the pulse which arrives at the input 11 when each of the glow transfer tubes has the discharge located on the 9th cathode. The operation of the circuit of FIG. 2 will be discussed with reference to the waveforms of FIG. 2A, assuming the condition that the input pulse is the 1,0Q0th pulse.

The pulse generated at 12, in response to the pulse at input 11, provides a pair of squarewave pulses with the leading squarewave applied to guides GI and the lagging squarewave applied to guides GI and G2 The negative squarewave applied to guides Gl causes the glow discharge in tube V to transfer from the ninth cathode to the adjacent first guide. The immediately following squarewave applied to the guides GI and also to guides G2 of tube V transfers the discharge in tube V from the first guide adjacent to the ninth cathode to the second guide. At the same time, the action of this pulse at the first guides G2 of the second transfer tube V transfers the discharge from the ninth cathode of tube V to the adjacent first guide. When the second squarewave pulse on guides G1 returns to the base line, the discharge in tube V is transferred to the next digit cathode which is cathode K The arrival of the discharge at cathode K provides current through resistor 31 and, hence, cathode K assumes a more positive potential, with the voltage rise limited to the necessary value by grid current in T The increase of potential of K carries, of course, the grid 30 of triode T up with it and renders this triode conducting, thereby producing a drop in potential at the anode 33. This trip in potential of anode 33 is transferred through capacitor 35 as a negative pulse to both guides G2 of transfer tube V and guides 63 of transfer tube V In tube V the discharge is then moved from the first guide GZ adjacent to the ninth cathode to the second guide adjacent to the zero cathode K Since it is the trailing edge of the pulse applied to GI and GZ which transfers the discharge in tube V to cathode K then the leading edge of the pulse output from T is coincident in time with the trailing edge of this previous squarewave. Hence, the negative voltage applied to guides GZ is removed simultaneously with the application of the negative pulse to guides 62;, and the timing sequence for transfer of the discharge in tube V from the first guide pin to the second guide pin is precise.

Since the discharge remains on cathode K then the anode of triode T remains at the decreased value and, hence, further action is required in order to decrease the negative voltage on guides G2 and, thus, transfer the discharge in tube V to the tenth cathode, K This action is provided by the RC. time constant of capacitor 35 and resistors 36 and 37 in series. The negative voltage on guides 62;, decreases at a rate controlled by this time constant. When this voltage falls below an amplitude designated as e in FIG. 2A, the negative bias on the guides GZ is insufiicient to maintain the discharge at this guide and it transfers to the next adjacent cathode K The arrival of the discharge on K initiates the same action in triode T which previously took place in T and hence a negative pulse is applied to guides (33 Since the value of 2 may differ for various glow transfer tubes, some provision is required to insure that the negative pulse 63 has not decreased to the point where the discharge in tube V is relaxed back to the original ninth cathode before the second transfer pulse G3 is applied. This condition is assured by the action of the attenuator formed by the resistors 36 and 37, such that the negative pulse applied to cathode GZ is smaller in amplitude than the pulse applied to 63 If, in fact, the transfer of the discharge to cathode K is effected before the termination of the pulse on 63 no adverse effect results, since when the 63 voltage does decrease, there will still remain a pulse on G3,; to transfer the discharge from the first guide to the second guide of tube V In the action of the third glow transfer tube V the time constant, formed in this stage by resistor 46 and the capacitor 45, causes the decay of the negative voltage applied to 63;, and when this voltage decreases below the value e for tube V the discharge will transfer from the second guide cathode to the tenth cathode, K

The output of the three cascaded transfer tubes is taken directly from the cathode K and the output pulse occurs as a step increase in voltage as indicated in FIG. 2A. This output voltage may be applied to a discriminator which is adapted to distinguish between a positive voltage step occurring at intervals separated by the time required for 1,000 pulses, as opposed to any step voltages occurring at more frequent intervals. Typically a discriminator may be formed as an integration circuit with a relatively long time constant.

Referring now to FIG. 2B, the waveforms at the same points as in FIG. 2A are shown for a pulse applied to the input 11 of pulse generator 12 when each of the glow transfer tubes, V V and V are in their zero position; that is, the glow discharge is located on cathodes K K and K respectively. In response to the pulse on input 11, the generator 12 provides the squarewave output pulses on outputs 13 and 14. These pulses applied to guides GI and 61;, on tube V advance the discharge from the zero cathode, K to the first digit cathode. Thus, the cathode K which had been conducting decreases in potential when the discharge is transferred away from it. The decrease of potential in K results in a positive pulse being applied from the output of triode T to guides 62;, and 63 Since these pulses are positive in polarity, no action in terms of discharge transfer is occasioned by them. The negative pulse applied to guide 62 of tube V transfers the discharge from the K cathode to the first guide adjacent to the K cathode for the duration of the squarewave pulse. At the conclusion of this pulse, the discharge returns to cathode K The action of the cathode K provides a positive pulse through triode T and, hence, to guide-s 63;, of tube V The sharp, negative-going, trailing edge of the positive pulse on G3;, will cause the discharge on cathode K to transfer to the preceding second guide cathode, until the negative amplitude has decreased below e, at which point the discharge relaxes back to the cathode K This provides on the output a relatively short duration negative squarewave.

The output from the third decade may be applied through a discriminator, such as an integrating time constant either to any one of the usual counting circuits, such as registers, decade counters, or the like, or it may be applied to a pulse generator of the type used at the input to the present circuit, such as pulse generator 12, to drive another set of three cascaded glow transfer tubes. Since the input pulse rate has been scaled down by a factor of 1,000 at the output of the first three cascaded tubes, in many instances a slower type of circuitry may be employed.

While the invention has been described in terms of RC. interstage coupling, direct coupling may also be employed. In this instance, conventional voltage level shifting circuits, such as neon tubes must be used in order to attain the appropriate D.C. levels at the inputs to the following stages.

While the circuits above have been described in terms of three stages, they can be expanded to more than three stages by applying appropriate criteria to the selection of the R.C. time constant of the interstage coupling networks. If the RC. time constant is made smaller than the minimum interval between incoming pulses, then the circuits may be expanded to include further stages. A five stage circuit is illustrated in FIG. 3, with the ap propriate waveforms shown in FIG. 4. For purposes of simplicity, each of the stages is shown as having three cathodes, rather than the conventional ten. A ten cathode stage, which would provide a decade unit, will operate in precisely the same fashion.

Referring now to FIG. 3, five stages are shown with the glow transfer tubes being designated V V V V and V The basic circuit arrangement is precisely the same as that of the circuit illustrated in FIG. 1. The interstage coupling capacitors and resistors are designated C and R, respectively, with different subscripts for each stage. In the waveform diagram of FIG. 4, the state of the glow in each of the glow transfer tubes is indicated both before and after each incoming pulse. Thus, prior to the arrival of the first pulse at the input, each of the glow transfer tubes have the glow discharge located on the second cathode of each tube, and this is indicated by the numerals 22222 before the first pulse. The first pulse then shifts the discharge in all the glow transfer tubes to the output or Zero cathode, which is designated in the schematic of FIG. 3 as the K cathode. The second pulse then transfers the discharge in only tube V from the zero to the first cathode, hence the designation 00001. This same nomenclature is followed throughout with reference to the incoming pulses. The operation of this circuit 7 follows the operation of the circuit described with reference to FIG. 1. The dotted lines indicate the 2 level for each of the stages. The point at which the time constant becomes critical occurs with reference to the signals on the guides G3 and G4 1. At point a on this waveform, a negative going pulse exceeding the e level for stage V is generated as a result of transfer of discharge in tube V to cathode K In the waveform as shown, the time constant is within the desired limit, that is, it is less than the interval between input pulses. Thus, the negative pulse decays from point a to point 11 and a positive pulse of short duration then occurs as a result of the temporary removal of the discharge from cathode K effected by the second input pulse. When the discharge returns to cathode K a negative pulse is again impressed on the guides 63 and G4 1. If the decay of the first negative pulse from point a to point b is not sufficiently rapid, then the following negative pulse may attain an amplitude in excess of e, which would then provide a negative pulse on cathode K which would be carried through to guides 64 and G5 1. The combination of the negative pulse at point a on guides 64 with this latter pulse on 64 would constitute the necessary sequence to transfer the glow which had just arrived on cathode K, to the number one cathode in stage V,. This latter transfer is, of course, improper and would constitute an error in the counting. Thus, by appropriate selection of these critical time constants matched with careful setting of the e level in each stage, this source of false pulses is eliminated and the overall circuit may be extended beyond three, four, or five stages.

Having described the invention, various modifications and departures will now occur to those skilled in this art, and the invention herein should be construed as limited only bythe spirit and scope of the appended claims.

What is claimed is:

1. Apparatus for counting a series of applied pulses comprising a plurality of glow transfer counter tubes, in serial cascade, each of said counter tubes being characterized by having a plurality of digit cathodes and first and second guide cathodes intermediate each of said digit cathodes; a pulse generator having an input and first and second independent outputs, said applied pulses being connected to said input, said pulse generator being adapted to produce in response to each of said input pulses substantially square wave output pulses on said first and second outputs, said square wave output pulse on said second output having a leading edge in substantial time coincidence with the trailing edge of said square wave pulse on said first output, said first output of said pulse generator being connected directly to said first guide cathodes of a first one of said counter tubes, said second output of said pulse generator being connected directly to said second guide cathodes of said first one of said counter tubes and to said first guide cathodes of said second one of said counter tubes; means for biasing negatively one of said digit cathodes in each of said counter tubes; coupling means for capacitively coupling each of said negatively biased digit cathodes to the said second guide cathodes of the next successive one of said plurality of counter tubes and to the said first guide cathodes of the second successive one of said counter tubes, said coupling means having a coupling time constant less than the minimum interval between pulses in said applied series.

2. Apparatus in accordance with claim 1 wherein each of said coupling means includes an attenuator between each of said negatively biased cathodes and the said second guide cathodes of the next successive one of said plurality of decade tubes.

3. Apparatus for counting applied pulses comprising, first, second, and third glow transfer counting tubes, each of said counting tubes being characterized by having 11 digit cathodes; first and second guide cathodes disposed intermediate each of said digit cathodes, 11-1 of said digit cathodes in each of said counting tubes being connected irectly to a reference potential junction, at source of negative bias voltage connected directly to the nth digit cathodes of each of said first and second counting tubes; a pulse generator having an input and first and second independent outputs, said pulse generator input being adapted to receive said applied pulses, said pulse generator providing in response to each of said input pulses first and second output pulses on said independent outputs, said first output pulse from said pulse generator being connected directly to said first guide cathodes of said first counting tube and said second pulse output from said pulse generator being connected directly to said second guide'cathodes of said first counting tube and said first guide cathodes of said second counting tube; first coupling means connected to said nth cathode of said first counting tube and adapted to couple electrically said nth cathode of said first counting tube through an R.C. network to said second guide cathodes of said second counting tube and to said first guide cathodes of said third counting tube; second coupling means connected directly to said nth cathode of said second counting tube, said second coupling means being adapted to couple said nth cathode of said second counting tube through an RC. network to said second guide cathodes of said third counting tube; output circuit means connected directly to said nth cathode of said third counting tube to provide a circuit output, said first coupling means including a first attenuator between said nth cathode of said first counting tube and said second guide cathodes of said second counting tube and wherein said coupling means includes an attenuator between said nth cathode of said second counting tube and said second guide cathodes of said third counting tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,679,978 Kandiah June 1, 1954 

1. APPARATUS FOR COUNTING A SERIES OF APPLIED PULSES COMPRISING A PLURALITY OF GLOW TRANSFER COUNTER TUBES, IN SERIAL CASCADE, EACH OF SAID COUNTER TUBES BEING CHARACTERIZED BY HAVING A PLURALITY OF DIGIT CATHODES AND FIRST AND SECOND GUIDE CATHODES INTERMEDIATE EACH OF SAID DIGIT CATHODES; A PULSE GENERTOR HAVING AN INPUT AND FIRST AND SECOND INDEPENDENT OUTPUTS, SAID APPLIED PULSES BEING CONNECTED TO SAID INPUT, SAID PULSE GENERATOR BEING ADAPTED TO PRODUCE IN RESPONSE TO EACH OF SAID INPUT PULSES SUBSTANTIALLY SEQUARE WAVE OUTPUT PULSES ON SAID FIRST AND SECOND OUTPUTS, SAID SQUARE WAVE OUTPUT PULSE ON SAID SECOND OUTPUT HAVING A LEADING EDGE IN SUBSTANTIAL TIME COINCIDENCE WITH THE TRAILING EDGE OF SID SQUARE WAVE PULSE ON SAID FIRST OUTPUT, SAID FIRST OUTPUT OF SAID PULSES GENERATOR BEING CONNECTED DIRECTLY TO SAID FIRST GUIDE CATHODES OF A FIRST ONE OF SAID COUNTER TUBES, SAID SECOND OUTPUT OF SAID PULSE GENERATOR BEING CONNECTED DIRECTLY TO SAID SECOND GUIDE CATHODES OF SAID FIRST ONE OF SAID COUNTER TUBES AND TO SAID FIRST GUIDE CATHODES OF SAID SECOND ONE OF SAID COUNTER TUBES; MEANS FOR BIASING NEGATIVELY ONE OF SAID DIGIT CATHODES IN EACH OF SAID COUNTER TUBES; COUPLING MEANS FOR CAPACITIVELY COUPLING EACH OF SAID NEGATIVELY BIASED DIGIT CATHODES TO THE SAID SECOND GUIDE CATHODES OF THE NEXT SUCCESSIVE ONE OF SAID PLURALITY OF COUNTER TUBES AND TO THE SAID FIRST GUIDE CTHODES OF THE SECOND SUCCESSIVE ONE OF SAID COUNTER TUBES, SAID COUPLING MEAND HAVING A COUPLING TIME CONSTANT LESS THAN THE MINIMUM INTERVAL BETWEEN PULSES IN SAID APPLIED SERIES. 